hello, from the tags i can see you are using bootstrap.
you can use rows and cols like the example below.
Also please have a look at bootstrap grid system it will help you alot:
Grid system · Bootstrap[
^]
Example:
<div class="row">
<div class="col-md-6">
<div class = "iframe-container">
<iframe width="100%" height="180" style="border: 2px solid #cccccc;" src="https://thingspeak.com/channels/929272/charts/1?bgcolor=%23ffffff&color=%23d62020&dynamic=true&results=60&type=line&update=15">
</iframe>
</div>
</div>
<div class="col-md-6">
<div class = "iframe-container">
<iframe width="100%" height="180" style="border: 2px solid #cccccc;" src="https://thingspeak.com/channels/929272/charts/2?bgcolor=%23ffffff&color=%23d62020&dynamic=true&results=60&type=line&update=15">
</iframe>
</div>
</div>
</div>
<div class="row">
<div class="col-md-12">
<div class="row">
<div class="col-md-12">
<div class = "iframe-container">
<iframe width="100%" height="180" style="border: 2px solid #cccccc;" src="https://thingspeak.com/channels/929272/charts/8?bgcolor=%23ffffff&color=%23d62020&dynamic=true&results=60&type=line&update=15"></iframe>
</div>
</div>
</div>
<div class="row">
<div class="col-md-1 offset-md-6">
<div class = "wrapper" align = "center">
<div class="btn-group" id="toggle_event_editing">
<button type="button" class="btn btn-danger locked_active">OFF</button>
<button type="button" class="btn btn-success unlocked_inactive">ON</button>
</div>
<div class="alert alert-info" id="switch_status">Switched off.</div>
</div>
</div>
</div>
</div>
</div>